The present invention relates to an improved apparatus for transferring workpieces automatically into or out of a press machine.
Conventionally, in this kind of automatic transfer systems, the workpieces to be transferred into the press machine have to be suitably positioned in a feeding station and then mounted on a carriage. Thereafter, the carriage with the workpiece mounted thereon is moved by a pneumatic cylinder or the like to transfer the workpiece into the press machine. However, such a system employing cylinder means for transferring a carriage is affected strongly by inertia forces of the carriage and members associated therewith thereby resulting in inaccurate stopping positions and unstable transfer velocities along the transfer path. Also, such a system is not suitable for a high speed transfer due to its inconsistent movement during the starting and stopping stages. Recently, to improve drawbacks which accompany such conventional systems and to enable a high speed transfer of workpieces, a transfer machine was proposed in laidopen Japanese Pat. No. 107681/1975 published Aug. 25, 1975 in which a Scott-Russell mechanism is employed for transferring a carriage. This type of machine is advantageous in that, as shown in FIG. 4 curve (a) of the drawings attached hereto, an approximate sine-curve is drawn by its speed/location plotting, but this is disadvantageous in that the starting and stopping movements are inconsistent and considerable vibrations and impacts are caused as the foot portions of the sine-curve are not used.
Furthermore, there was also proposed another type of transfer machine, disclosed in laid-open Japanese Pat. No. 87874/1976 published July 31, 1976 which makes use of a crank mechanism and a rotary arm to transfer a carriage through a chain and gears. This type of machines can use a whole sine-curve for its speed characteristics, as shown in FIG. 4, curve (b) of the drawings attached hereto which results in a relatively consistent movements of the carriage during the starting and stopping stages, but on the other hand is accompanied by a serious drawback of inaccurate stop positions of the carriage due to the inertia forces thereof because relaxation of the chain and backlashes of a series of transmission gears and other mating parts reflect in the entireties thereof to the stop positions.